<s>
Portable	B-Application
Document	I-Application
Format	I-Application
(	O
PDF	B-Application
)	O
,	O
standardized	O
as	O
ISO	B-Application
32000	I-Application
,	O
is	O
a	O
file	O
format	O
developed	O
by	O
Adobe	O
in	O
1992	O
to	O
present	O
documents	O
,	O
including	O
text	O
formatting	O
and	O
images	O
,	O
in	O
a	O
manner	O
independent	O
of	O
application	B-Application
software	I-Application
,	O
hardware	B-Architecture
,	O
and	O
operating	B-General_Concept
systems	I-General_Concept
.	O
</s>
<s>
Based	O
on	O
the	O
PostScript	B-Language
language	I-Language
,	O
each	O
PDF	B-Application
file	I-Application
encapsulates	O
a	O
complete	O
description	O
of	O
a	O
fixed-layout	O
flat	O
document	O
,	O
including	O
the	O
text	O
,	O
fonts	O
,	O
vector	O
graphics	O
,	O
raster	B-Algorithm
images	I-Algorithm
and	O
other	O
information	O
needed	O
to	O
display	O
it	O
.	O
</s>
<s>
PDF	B-Application
has	O
its	O
roots	O
in	O
"	O
The	O
Camelot	O
Project	O
"	O
initiated	O
by	O
Adobe	O
co-founder	O
John	O
Warnock	O
in	O
1991	O
.	O
</s>
<s>
PDF	B-Application
was	O
standardized	O
as	O
ISO	B-Application
32000	I-Application
in	O
2008	O
.	O
</s>
<s>
PDF	B-Application
files	I-Application
may	O
contain	O
a	O
variety	O
of	O
content	O
besides	O
flat	O
text	O
and	O
graphics	O
including	O
logical	O
structuring	O
elements	O
,	O
interactive	O
elements	O
such	O
as	O
annotations	O
and	O
form-fields	O
,	O
layers	O
,	O
rich	O
media	O
(	O
including	O
video	O
content	O
)	O
,	O
three-dimensional	O
objects	O
using	O
U3D	O
or	O
PRC	O
,	O
and	O
various	O
other	O
data	O
formats	O
.	O
</s>
<s>
The	O
PDF	B-Application
specification	O
also	O
provides	O
for	O
encryption	O
and	O
digital	O
signatures	O
,	O
file	O
attachments	O
,	O
and	O
metadata	O
to	O
enable	O
workflows	B-Operating_System
requiring	O
these	O
features	O
.	O
</s>
<s>
Adobe	O
Systems	O
made	O
the	O
PDF	B-Application
specification	O
available	O
free	O
of	O
charge	O
in	O
1993	O
.	O
</s>
<s>
In	O
the	O
early	O
years	O
PDF	B-Application
was	O
popular	O
mainly	O
in	O
desktop	O
publishing	O
workflows	B-Operating_System
,	O
and	O
competed	O
with	O
a	O
variety	O
of	O
formats	O
such	O
as	O
DjVu	O
,	O
Envoy	B-Application
,	O
Common	O
Ground	O
Digital	O
Paper	O
,	O
Farallon	O
Replica	O
and	O
even	O
Adobe	O
's	O
own	O
PostScript	B-Language
format	O
.	O
</s>
<s>
PDF	B-Application
was	O
a	O
proprietary	O
format	O
controlled	O
by	O
Adobe	O
until	O
it	O
was	O
released	O
as	O
an	O
open	O
standard	O
on	O
July	O
1	O
,	O
2008	O
,	O
and	O
published	O
by	O
the	O
International	O
Organization	O
for	O
Standardization	O
as	O
ISO	B-General_Concept
32000-1:2008	O
,	O
at	O
which	O
time	O
control	O
of	O
the	O
specification	O
passed	O
to	O
an	O
ISO	B-General_Concept
Committee	O
of	O
volunteer	O
industry	O
experts	O
.	O
</s>
<s>
In	O
2008	O
,	O
Adobe	O
published	O
a	O
Public	O
Patent	O
License	O
to	O
ISO	B-Application
32000-1	I-Application
granting	O
royalty-free	O
rights	O
for	O
all	O
patents	O
owned	O
by	O
Adobe	O
that	O
are	O
necessary	O
to	O
make	O
,	O
use	O
,	O
sell	O
,	O
and	O
distribute	O
PDF-compliant	O
implementations	O
.	O
</s>
<s>
PDF	B-Application
1.7	O
,	O
the	O
sixth	O
edition	O
of	O
the	O
PDF	B-Application
specification	O
that	O
became	O
ISO	B-Application
32000-1	I-Application
,	O
includes	O
some	O
proprietary	O
technologies	O
defined	O
only	O
by	O
Adobe	O
,	O
such	O
as	O
Adobe	B-Language
XML	I-Language
Forms	I-Language
Architecture	I-Language
(	O
XFA	B-Language
)	O
and	O
JavaScript	B-Language
extension	O
for	O
Acrobat	O
,	O
which	O
are	O
referenced	O
by	O
ISO	B-Application
32000-1	I-Application
as	O
normative	O
and	O
indispensable	O
for	O
the	O
full	O
implementation	O
of	O
the	O
ISO	B-Application
32000-1	I-Application
specification	O
.	O
</s>
<s>
Many	O
of	O
them	O
are	O
also	O
not	O
supported	O
by	O
popular	O
third-party	O
implementations	O
of	O
PDF	B-Application
.	O
</s>
<s>
In	O
December	O
2020	O
,	O
the	O
second	O
edition	O
of	O
PDF	B-Application
2.0	O
,	O
ISO	O
32000-2:2020	O
,	O
was	O
published	O
,	O
including	O
clarifications	O
,	O
corrections	O
,	O
and	O
critical	O
updates	O
to	O
normative	O
references	O
.	O
</s>
<s>
ISO	B-General_Concept
's	I-General_Concept
publication	O
of	O
ISO	O
32000-2	O
in	O
2017	O
ended	O
the	O
24-year	O
tradition	O
of	O
the	O
latest	O
PDF	B-Application
specification	O
being	O
freely	O
available	O
from	O
Adobe	O
.	O
</s>
<s>
Starting	O
in	O
April	O
,	O
2023	O
,	O
to	O
provide	O
PDF	B-Application
developers	O
and	O
stakeholders	O
with	O
their	O
accustomed	O
level	O
of	O
access	O
,	O
the	O
PDF	B-Application
Association	O
and	O
its	O
sponsors	O
made	O
ISO	O
32000-2	O
available	O
for	O
download	O
at	O
no	O
cost	O
.	O
</s>
<s>
A	O
PDF	B-Application
file	I-Application
is	O
often	O
a	O
combination	O
of	O
vector	O
graphics	O
,	O
text	O
,	O
and	O
bitmap	B-Algorithm
graphics	I-Algorithm
.	O
</s>
<s>
The	O
basic	O
types	O
of	O
content	O
in	O
a	O
PDF	B-Application
are	O
:	O
</s>
<s>
Typeset	O
text	O
stored	O
as	O
content	O
streams	B-Architecture
(	O
i.e.	O
,	O
not	O
encoded	O
in	O
plain	O
text	O
)	O
;	O
</s>
<s>
In	O
later	O
PDF	B-Application
revisions	O
,	O
a	O
PDF	B-Application
document	O
can	O
also	O
support	O
links	O
(	O
inside	O
document	O
or	O
web	O
page	O
)	O
,	O
forms	O
,	O
JavaScript	B-Language
(	O
initially	O
available	O
as	O
a	O
plugin	O
for	O
Acrobat	O
3.0	O
)	O
,	O
or	O
any	O
other	O
types	O
of	O
embedded	O
contents	O
that	O
can	O
be	O
handled	O
using	O
plug-ins	O
.	O
</s>
<s>
PDF	B-Application
combines	O
three	O
technologies	O
:	O
</s>
<s>
An	O
equivalent	O
subset	O
of	O
the	O
PostScript	B-Language
page	O
description	O
programming	O
language	O
but	O
in	O
declarative	O
form	O
,	O
for	O
generating	O
the	O
layout	O
and	O
graphics	O
.	O
</s>
<s>
A	O
structured	O
storage	O
system	O
to	O
bundle	O
these	O
elements	O
and	O
any	O
associated	O
content	O
into	O
a	O
single	O
file	O
,	O
with	O
data	B-General_Concept
compression	I-General_Concept
where	O
appropriate	O
.	O
</s>
<s>
PostScript	B-Language
is	O
a	O
page	O
description	O
language	O
run	O
in	O
an	O
interpreter	B-Application
to	O
generate	O
an	O
image	O
,	O
a	O
process	O
requiring	O
many	O
resources	O
.	O
</s>
<s>
PDF	B-Application
is	O
largely	O
based	O
on	O
PostScript	B-Language
but	O
simplified	O
to	O
remove	O
flow	O
control	O
features	O
like	O
these	O
,	O
while	O
graphics	O
commands	O
equivalent	O
to	O
lineto	O
remain	O
.	O
</s>
<s>
Historically	O
,	O
the	O
PostScript-like	O
PDF	B-Application
code	O
is	O
generated	O
from	O
a	O
source	O
PostScript	B-Language
file	O
.	O
</s>
<s>
The	O
graphics	O
commands	O
that	O
are	O
output	O
by	O
the	O
PostScript	B-Language
code	O
are	O
collected	O
and	O
tokenized	B-Application
.	O
</s>
<s>
Therefore	O
,	O
the	O
entire	O
PostScript	B-Language
world	O
(	O
fonts	O
,	O
layout	O
,	O
measurements	O
)	O
remains	O
intact	O
.	O
</s>
<s>
As	O
a	O
document	O
format	O
,	O
PDF	B-Application
has	O
several	O
advantages	O
over	O
PostScript	B-Language
:	O
</s>
<s>
PDF	B-Application
contains	O
tokenized	B-Application
and	O
interpreted	O
results	O
of	O
the	O
PostScript	B-Language
source	O
code	O
,	O
for	O
direct	O
correspondence	O
between	O
changes	O
to	O
items	O
in	O
the	O
PDF	B-Application
page	O
description	O
and	O
changes	O
to	O
the	O
resulting	O
page	O
appearance	O
.	O
</s>
<s>
PDF	B-Application
(	O
since	O
version	O
1.4	O
)	O
supports	O
transparent	O
graphics	O
;	O
PostScript	B-Language
does	O
not	O
.	O
</s>
<s>
PostScript	B-Language
is	O
an	O
interpreted	B-Application
programming	I-Application
language	I-Application
with	O
an	O
implicit	O
global	O
state	O
,	O
so	O
instructions	O
accompanying	O
the	O
description	O
of	O
one	O
page	O
can	O
affect	O
the	O
appearance	O
of	O
any	O
following	O
page	O
.	O
</s>
<s>
Therefore	O
,	O
all	O
preceding	O
pages	O
in	O
a	O
PostScript	B-Language
document	O
must	O
be	O
processed	O
to	O
determine	O
the	O
correct	O
appearance	O
of	O
a	O
given	O
page	O
,	O
whereas	O
each	O
page	O
in	O
a	O
PDF	B-Application
document	O
is	O
unaffected	O
by	O
the	O
others	O
.	O
</s>
<s>
As	O
a	O
result	O
,	O
PDF	B-Language
viewers	I-Language
allow	O
the	O
user	O
to	O
quickly	O
jump	O
to	O
the	O
final	O
pages	O
of	O
a	O
long	O
document	O
,	O
whereas	O
a	O
PostScript	B-Language
viewer	O
needs	O
to	O
process	O
all	O
pages	O
sequentially	O
before	O
being	O
able	O
to	O
display	O
the	O
destination	O
page	O
(	O
unless	O
the	O
optional	O
PostScript	B-Language
Document	B-Language
Structuring	I-Language
Conventions	I-Language
have	O
been	O
carefully	O
compiled	O
and	O
included	O
)	O
.	O
</s>
<s>
PDF	B-Application
1.6	O
and	O
later	O
supports	O
interactive	O
3D	O
documents	O
embedded	O
in	O
a	O
PDF	B-Application
file	I-Application
:	O
3D	O
drawings	O
can	O
be	O
embedded	O
using	O
U3D	O
or	O
PRC	O
and	O
various	O
other	O
data	O
formats	O
.	O
</s>
<s>
A	O
PDF	B-Application
file	I-Application
is	O
organized	O
using	O
ASCII	B-Protocol
characters	I-Protocol
,	O
except	O
for	O
certain	O
elements	O
that	O
may	O
have	O
binary	O
content	O
.	O
</s>
<s>
The	O
file	O
starts	O
with	O
a	O
header	O
containing	O
a	O
magic	O
number	O
(	O
as	O
a	O
readable	O
string	O
)	O
and	O
the	O
version	O
of	O
the	O
format	O
,	O
for	O
example	O
%	O
PDF-1.7	O
.	O
</s>
<s>
Streams	B-Architecture
,	O
usually	O
containing	O
large	O
amounts	O
of	O
optionally	O
compressed	O
binary	O
data	O
,	O
preceded	O
by	O
a	O
dictionary	B-Application
and	O
enclosed	O
between	O
the	O
stream	O
and	O
endstream	O
keywords	O
.	O
</s>
<s>
Beginning	O
with	O
PDF	B-Application
version	O
1.5	O
,	O
indirect	O
objects	O
(	O
except	O
other	O
streams	B-Architecture
)	O
may	O
also	O
be	O
located	O
in	O
special	O
streams	B-Architecture
known	O
as	O
object	O
streams	B-Architecture
(	O
marked	O
/Type	O
/ObjStm	O
)	O
.	O
</s>
<s>
This	O
technique	O
enables	O
non-stream	O
objects	O
to	O
have	O
standard	O
stream	O
filters	O
applied	O
to	O
them	O
,	O
reduces	O
the	O
size	O
of	O
files	O
that	O
have	O
large	O
numbers	O
of	O
small	O
indirect	O
objects	O
and	O
is	O
especially	O
useful	O
for	O
Tagged	O
PDF	B-Application
.	O
</s>
<s>
Object	O
streams	B-Architecture
do	O
not	O
support	O
specifying	O
an	O
object	O
's	O
generation	O
number	O
(	O
other	O
than	O
0	O
)	O
.	O
</s>
<s>
This	O
design	O
allows	O
for	O
efficient	O
random	B-General_Concept
access	I-General_Concept
to	O
the	O
objects	O
in	O
the	O
file	O
,	O
and	O
also	O
allows	O
for	O
small	O
changes	O
to	O
be	O
made	O
without	O
rewriting	O
the	O
entire	O
file	O
(	O
incremental	O
update	O
)	O
.	O
</s>
<s>
Before	O
PDF	B-Application
version	O
1.5	O
,	O
the	O
table	O
would	O
always	O
be	O
in	O
a	O
special	O
ASCII	B-Protocol
format	O
,	O
be	O
marked	O
with	O
the	O
xref	O
keyword	O
,	O
and	O
follow	O
the	O
main	O
body	O
composed	O
of	O
indirect	O
objects	O
.	O
</s>
<s>
Version	O
1.5	O
introduced	O
optional	O
cross-reference	O
streams	B-Architecture
,	O
which	O
have	O
the	O
form	O
of	O
a	O
standard	O
stream	O
object	O
,	O
possibly	O
with	O
filters	O
applied	O
.	O
</s>
<s>
Such	O
a	O
stream	O
may	O
be	O
used	O
instead	O
of	O
the	O
ASCII	B-Protocol
cross-reference	O
table	O
and	O
contains	O
the	O
offsets	O
and	O
other	O
information	O
in	O
binary	O
format	O
.	O
</s>
<s>
The	O
%%EOF	O
end-of-file	B-Language
marker	O
.	O
</s>
<s>
If	O
a	O
cross-reference	O
stream	O
is	O
not	O
being	O
used	O
,	O
the	O
footer	O
is	O
preceded	O
by	O
the	O
trailer	O
keyword	O
followed	O
by	O
a	O
dictionary	B-Application
containing	O
information	O
that	O
would	O
otherwise	O
be	O
contained	O
in	O
the	O
cross-reference	O
stream	O
object	O
's	O
dictionary	B-Application
:	O
</s>
<s>
Within	O
each	O
page	O
,	O
there	O
are	O
one	O
or	O
multiple	O
content	O
streams	B-Architecture
that	O
describe	O
the	O
text	O
,	O
vector	O
and	O
images	O
being	O
drawn	O
on	O
the	O
page	O
.	O
</s>
<s>
The	O
content	O
stream	O
is	O
stack-based	B-Language
,	O
similar	O
to	O
PostScript	B-Language
.	O
</s>
<s>
There	O
are	O
two	O
layouts	O
to	O
the	O
PDF	B-Application
files	I-Application
:	O
non-linearized	O
(	O
not	O
"	O
optimized	O
"	O
)	O
and	O
linearized	O
(	O
"	O
optimized	O
"	O
)	O
.	O
</s>
<s>
Non-linearized	O
PDF	B-Application
files	I-Application
can	O
be	O
smaller	O
than	O
their	O
linear	O
counterparts	O
,	O
though	O
they	O
are	O
slower	O
to	O
access	O
because	O
portions	O
of	O
the	O
data	O
required	O
to	O
assemble	O
pages	O
of	O
the	O
document	O
are	O
scattered	O
throughout	O
the	O
PDF	B-Application
file	I-Application
.	O
</s>
<s>
Linearized	O
PDF	B-Application
files	I-Application
(	O
also	O
called	O
"	O
optimized	O
"	O
or	O
"	O
web	O
optimized	O
"	O
PDF	B-Application
files	I-Application
)	O
are	O
constructed	O
in	O
a	O
manner	O
that	O
enables	O
them	O
to	O
be	O
read	O
in	O
a	O
Web	O
browser	O
plugin	O
without	O
waiting	O
for	O
the	O
entire	O
file	O
to	O
download	O
,	O
since	O
all	O
objects	O
required	O
for	O
the	O
first	O
page	O
to	O
display	O
are	O
optimally	O
organized	O
at	O
the	O
start	O
of	O
the	O
file	O
.	O
</s>
<s>
PDF	B-Application
files	I-Application
may	O
be	O
optimized	O
using	O
Adobe	B-Application
Acrobat	I-Application
software	O
or	O
QPDF	B-Language
.	O
</s>
<s>
The	O
basic	O
design	O
of	O
how	O
graphics	O
are	O
represented	O
in	O
PDF	B-Application
is	O
very	O
similar	O
to	O
that	O
of	O
PostScript	B-Language
,	O
except	O
for	O
the	O
use	O
of	O
transparency	O
,	O
which	O
was	O
added	O
in	O
PDF	B-Application
1.4	O
.	O
</s>
<s>
PDF	B-Application
graphics	O
use	O
a	O
device-independent	B-Operating_System
Cartesian	O
coordinate	O
system	O
to	O
describe	O
the	O
surface	O
of	O
a	O
page	O
.	O
</s>
<s>
A	O
PDF	B-Application
page	O
description	O
can	O
use	O
a	O
matrix	B-Architecture
to	O
scale	O
,	O
rotate	O
,	O
or	O
skew	B-Algorithm
graphical	O
elements	O
.	O
</s>
<s>
A	O
key	O
concept	O
in	O
PDF	B-Application
is	O
that	O
of	O
the	O
graphics	O
state	O
,	O
which	O
is	O
a	O
collection	O
of	O
graphical	O
parameters	O
that	O
may	O
be	O
changed	O
,	O
saved	O
,	O
and	O
restored	O
by	O
a	O
page	O
description	O
.	O
</s>
<s>
PDF	B-Application
has	O
(	O
as	O
of	O
version	O
2.0	O
)	O
25	O
graphics	O
state	O
properties	O
,	O
of	O
which	O
some	O
of	O
the	O
most	O
important	O
are	O
:	O
</s>
<s>
As	O
in	O
PostScript	B-Language
,	O
vector	O
graphics	O
in	O
PDF	B-Application
are	O
constructed	O
with	O
paths	O
.	O
</s>
<s>
Unlike	O
PostScript	B-Language
,	O
PDF	B-Application
does	O
not	O
allow	O
a	O
single	O
path	O
to	O
mix	O
text	O
outlines	O
with	O
lines	O
and	O
curves	O
.	O
</s>
<s>
PDF	B-Application
supports	O
several	O
types	O
of	O
patterns	O
.	O
</s>
<s>
Beginning	O
with	O
PDF	B-Application
1.3	O
there	O
is	O
also	O
a	O
shading	O
pattern	O
,	O
which	O
draws	O
continuously	O
varying	O
colors	O
.	O
</s>
<s>
Raster	B-Algorithm
images	I-Algorithm
in	O
PDF	B-Application
(	O
called	O
Image	O
XObjects	O
)	O
are	O
represented	O
by	O
dictionaries	B-Application
with	O
an	O
associated	O
stream	O
.	O
</s>
<s>
The	O
dictionary	B-Application
describes	O
the	O
properties	O
of	O
the	O
image	O
,	O
and	O
the	O
stream	O
contains	O
the	O
image	O
data	O
.	O
</s>
<s>
(	O
Less	O
commonly	O
,	O
small	O
raster	B-Algorithm
images	I-Algorithm
may	O
be	O
embedded	O
directly	O
in	O
a	O
page	O
description	O
as	O
an	O
inline	O
image	O
.	O
)	O
</s>
<s>
Image	O
filters	O
supported	O
in	O
PDF	B-Application
include	O
the	O
following	O
general-purpose	O
filters	O
:	O
</s>
<s>
ASCII85Decode	O
,	O
a	O
filter	O
used	O
to	O
put	O
the	O
stream	O
into	O
7-bit	B-Protocol
ASCII	I-Protocol
,	O
</s>
<s>
FlateDecode	O
,	O
a	O
commonly	O
used	O
filter	O
based	O
on	O
the	O
deflate	B-Algorithm
algorithm	O
defined	O
in	O
(	O
deflate	B-Algorithm
is	O
also	O
used	O
in	O
the	O
gzip	B-Application
,	O
PNG	O
,	O
and	O
zip	B-General_Concept
file	I-General_Concept
formats	I-General_Concept
among	O
others	O
)	O
;	O
introduced	O
in	O
PDF	B-Application
1.2	O
;	O
it	O
can	O
use	O
one	O
of	O
two	O
groups	O
of	O
predictor	O
functions	O
for	O
more	O
compact	O
zlib/deflate	O
compression	O
:	O
Predictor	O
2	O
from	O
the	O
TIFF	O
6.0	O
specification	O
and	O
predictors	O
(	O
filters	O
)	O
from	O
the	O
PNG	O
specification	O
(	O
)	O
,	O
</s>
<s>
LZWDecode	O
,	O
a	O
filter	O
based	O
on	O
LZW	B-Algorithm
Compression	I-Algorithm
;	O
it	O
can	O
use	O
one	O
of	O
two	O
groups	O
of	O
predictor	O
functions	O
for	O
more	O
compact	O
LZW	B-Algorithm
compression	I-Algorithm
:	O
Predictor	O
2	O
from	O
the	O
TIFF	O
6.0	O
specification	O
and	O
predictors	O
(	O
filters	O
)	O
from	O
the	O
PNG	O
specification	O
,	O
</s>
<s>
RunLengthDecode	O
,	O
a	O
simple	O
compression	O
method	O
for	O
streams	B-Architecture
with	O
repetitive	O
data	O
using	O
the	O
run-length	B-Algorithm
encoding	I-Algorithm
algorithm	O
and	O
the	O
image-specific	O
filters	O
,	O
</s>
<s>
DCTDecode	O
,	O
a	O
lossy	B-Algorithm
filter	O
based	O
on	O
the	O
JPEG	O
standard	O
,	O
</s>
<s>
CCITTFaxDecode	O
,	O
a	O
lossless	B-Algorithm
bi-level	B-Algorithm
(	O
black/white	O
)	O
filter	O
based	O
on	O
the	O
Group	O
3	O
or	O
Group	O
4	O
CCITT	O
(	O
ITU-T	O
)	O
fax	O
compression	O
standard	O
defined	O
in	O
ITU-T	O
T.4	O
and	O
T.6	O
,	O
</s>
<s>
JPXDecode	O
,	O
a	O
lossy	B-Algorithm
or	O
lossless	B-Algorithm
filter	O
based	O
on	O
the	O
JPEG	O
2000	O
standard	O
,	O
introduced	O
in	O
PDF	B-Application
1.5	O
.	O
</s>
<s>
Normally	O
all	O
image	O
content	O
in	O
a	O
PDF	B-Application
is	O
embedded	O
in	O
the	O
file	O
.	O
</s>
<s>
But	O
PDF	B-Application
allows	O
image	O
data	O
to	O
be	O
stored	O
in	O
external	O
files	O
by	O
the	O
use	O
of	O
external	O
streams	B-Architecture
or	O
Alternate	O
Images	O
.	O
</s>
<s>
Standardized	O
subsets	O
of	O
PDF	B-Application
,	O
including	O
PDF/A	B-General_Concept
and	O
PDF/X	O
,	O
prohibit	O
these	O
features	O
.	O
</s>
<s>
Text	O
in	O
PDF	B-Application
is	O
represented	O
by	O
text	O
elements	O
in	O
page	O
content	O
streams	B-Architecture
.	O
</s>
<s>
A	O
font	O
object	O
in	O
PDF	B-Application
is	O
a	O
description	O
of	O
a	O
digital	O
typeface	O
.	O
</s>
<s>
The	O
font	O
files	O
that	O
may	O
be	O
embedded	O
are	O
based	O
on	O
widely	O
used	O
standard	O
digital	O
font	O
formats	O
:	O
Type	O
1	O
(	O
and	O
its	O
compressed	O
variant	O
CFF	O
)	O
,	O
TrueType	O
,	O
and	O
(	O
beginning	O
with	O
PDF	B-Application
1.6	O
)	O
OpenType	O
.	O
</s>
<s>
Additionally	O
PDF	B-Application
supports	O
the	O
Type	O
3	O
variant	O
in	O
which	O
the	O
components	O
of	O
the	O
font	O
are	O
described	O
by	O
PDF	B-Application
graphic	O
operators	O
.	O
</s>
<s>
Fourteen	O
typefaces	O
,	O
known	O
as	O
the	O
standard	O
14	O
fonts	O
,	O
have	O
a	O
special	O
significance	O
in	O
PDF	B-Application
documents	I-Application
:	O
</s>
<s>
These	O
fonts	O
,	O
or	O
suitable	O
substitute	O
fonts	O
with	O
the	O
same	O
metrics	O
,	O
should	O
be	O
available	O
in	O
most	O
PDF	B-Language
readers	I-Language
,	O
but	O
they	O
are	O
not	O
guaranteed	O
to	O
be	O
available	O
in	O
the	O
reader	O
,	O
and	O
may	O
only	O
display	O
correctly	O
if	O
the	O
system	O
has	O
them	O
installed	O
.	O
</s>
<s>
Fonts	O
may	O
be	O
substituted	O
if	O
they	O
are	O
not	O
embedded	O
in	O
a	O
PDF	B-Application
.	O
</s>
<s>
(	O
Although	O
the	O
WinAnsi	O
and	O
MacRoman	O
encodings	O
are	O
derived	O
from	O
the	O
historical	O
properties	O
of	O
the	O
Windows	B-Application
and	O
Macintosh	B-Device
operating	B-General_Concept
systems	I-General_Concept
,	O
fonts	O
using	O
these	O
encodings	O
work	O
equally	O
well	O
on	O
any	O
platform	O
.	O
)	O
</s>
<s>
PDF	B-Application
can	O
specify	O
a	O
predefined	O
encoding	O
to	O
use	O
,	O
the	O
font	O
's	O
built-in	O
encoding	O
or	O
provide	O
a	O
lookup	O
table	O
of	O
differences	O
to	O
a	O
predefined	O
or	O
built-in	O
encoding	O
(	O
not	O
recommended	O
with	O
TrueType	O
fonts	O
)	O
.	O
</s>
<s>
The	O
encoding	O
mechanisms	O
in	O
PDF	B-Application
were	O
designed	O
for	O
Type	O
1	O
fonts	O
,	O
and	O
the	O
rules	O
for	O
applying	O
them	O
to	O
TrueType	O
fonts	O
are	O
complex	O
.	O
</s>
<s>
The	O
original	O
imaging	O
model	O
of	O
PDF	B-Application
was	O
,	O
like	O
PostScript	B-Language
's	O
,	O
opaque	O
:	O
each	O
object	O
drawn	O
on	O
the	O
page	O
completely	O
replaced	O
anything	O
previously	O
marked	O
in	O
the	O
same	O
location	O
.	O
</s>
<s>
In	O
PDF	B-Application
1.4	O
the	O
imaging	O
model	O
was	O
extended	O
to	O
allow	O
transparency	O
.	O
</s>
<s>
The	O
addition	O
of	O
transparency	O
to	O
PDF	B-Application
was	O
done	O
by	O
means	O
of	O
new	O
extensions	O
that	O
were	O
designed	O
to	O
be	O
ignored	O
in	O
products	O
written	O
to	O
PDF	B-Application
1.3	O
and	O
earlier	O
specifications	O
.	O
</s>
<s>
The	O
model	O
is	O
closely	O
aligned	O
with	O
the	O
features	O
of	O
Adobe	B-Language
Illustrator	I-Language
version	O
9	O
.	O
</s>
<s>
The	O
blend	B-Algorithm
modes	I-Algorithm
were	O
based	O
on	O
those	O
used	O
by	O
Adobe	B-Operating_System
Photoshop	I-Operating_System
at	O
the	O
time	O
.	O
</s>
<s>
When	O
the	O
PDF	B-Application
1.4	O
specification	O
was	O
published	O
,	O
the	O
formulas	O
for	O
calculating	O
blend	B-Algorithm
modes	I-Algorithm
were	O
kept	O
secret	O
by	O
Adobe	O
.	O
</s>
<s>
The	O
concept	O
of	O
a	O
transparency	O
group	O
in	O
PDF	B-Application
specification	O
is	O
independent	O
of	O
existing	O
notions	O
of	O
"	O
group	O
"	O
or	O
"	O
layer	O
"	O
in	O
applications	O
such	O
as	O
Adobe	B-Language
Illustrator	I-Language
.	O
</s>
<s>
A	O
"	O
tagged	O
"	O
PDF	B-Application
(	O
see	O
clause	O
14.8	O
in	O
ISO	B-Application
32000	I-Application
)	O
includes	O
document	O
structure	O
and	O
semantics	O
information	O
to	O
enable	O
reliable	O
text	O
extraction	O
and	O
accessibility	O
.	O
</s>
<s>
Technically	O
speaking	O
,	O
tagged	O
PDF	B-Application
is	O
a	O
stylized	O
use	O
of	O
the	O
format	O
that	O
builds	O
on	O
the	O
logical	O
structure	O
framework	O
introduced	O
in	O
PDF	B-Application
1.3	O
.	O
</s>
<s>
Tagged	O
PDF	B-Application
defines	O
a	O
set	O
of	O
standard	O
structure	O
types	O
and	O
attributes	O
that	O
allow	O
page	O
content	O
(	O
text	O
,	O
graphics	O
,	O
and	O
images	O
)	O
to	O
be	O
extracted	O
and	O
reused	O
for	O
other	O
purposes	O
.	O
</s>
<s>
Tagged	O
PDF	B-Application
is	O
not	O
required	O
in	O
situations	O
where	O
a	O
PDF	B-Application
file	I-Application
is	O
intended	O
only	O
for	O
print	O
.	O
</s>
<s>
Since	O
the	O
feature	O
is	O
optional	O
,	O
and	O
since	O
the	O
rules	O
for	O
Tagged	O
PDF	B-Application
were	O
relatively	O
vague	O
in	O
ISO	B-Application
32000-1	I-Application
,	O
support	O
for	O
tagged	O
PDF	B-Application
among	O
consuming	O
devices	O
,	O
including	O
assistive	O
technology	O
(	O
AT	O
)	O
,	O
is	O
uneven	O
as	O
of	O
2021	O
.	O
</s>
<s>
ISO	O
32000-2	O
,	O
however	O
,	O
includes	O
an	O
improved	O
discussion	O
of	O
tagged	O
PDF	B-Application
which	O
is	O
anticipated	O
to	O
facilitate	O
further	O
adoption	O
.	O
</s>
<s>
An	O
ISO-standardized	O
subset	O
of	O
PDF	B-Application
specifically	O
targeted	O
at	O
accessibility	O
,	O
PDF/UA	B-Protocol
,	O
was	O
first	O
published	O
in	O
2012	O
.	O
</s>
<s>
With	O
the	O
introduction	O
of	O
PDF	B-Application
version	O
1.5	O
(	O
2003	O
)	O
came	O
the	O
concept	O
of	O
Layers	O
.	O
</s>
<s>
Layers	O
,	O
more	O
formally	O
known	O
as	O
Optional	O
Content	O
Groups	O
(	O
OCGs	O
)	O
,	O
refer	O
to	O
sections	O
of	O
content	O
in	O
a	O
PDF	B-Application
document	O
that	O
can	O
be	O
selectively	O
viewed	O
or	O
hidden	O
by	O
document	O
authors	O
or	O
viewers	O
.	O
</s>
<s>
Basically	O
,	O
it	O
consists	O
of	O
an	O
Optional	O
Content	O
Properties	O
Dictionary	B-Application
added	O
to	O
the	O
document	O
root	O
.	O
</s>
<s>
This	O
dictionary	B-Application
contains	O
an	O
array	O
of	O
Optional	O
Content	O
Groups	O
(	O
OCGs	O
)	O
,	O
each	O
describing	O
a	O
set	O
of	O
information	O
and	O
each	O
of	O
which	O
may	O
be	O
individually	O
displayed	O
or	O
suppressed	O
,	O
plus	O
a	O
set	O
of	O
Optional	O
Content	O
Configuration	O
Dictionaries	B-Application
,	O
which	O
give	O
the	O
status	O
(	O
Displayed	O
or	O
Suppressed	O
)	O
of	O
the	O
given	O
OCGs	O
.	O
</s>
<s>
A	O
PDF	B-Application
file	I-Application
may	O
be	O
encrypted	O
,	O
for	O
security	O
,	O
in	O
which	O
case	O
a	O
password	O
is	O
needed	O
to	O
view	O
or	O
edit	O
the	O
contents	O
.	O
</s>
<s>
PDF	B-Application
2.0	O
defines	O
256-bit	O
AES	O
encryption	O
as	O
standard	O
for	O
PDF	B-Application
2.0	O
files	O
.	O
</s>
<s>
The	O
PDF	B-Application
Reference	O
also	O
defines	O
ways	O
that	O
third	O
parties	O
can	O
define	O
their	O
own	O
encryption	O
systems	O
for	O
PDF	B-Application
.	O
</s>
<s>
PDF	B-Application
files	I-Application
may	O
be	O
digitally	O
signed	O
,	O
to	O
provide	O
secure	O
authentication	O
;	O
complete	O
details	O
on	O
implementing	O
digital	O
signatures	O
in	O
PDF	B-Application
is	O
provided	O
in	O
ISO	O
32000-2	O
.	O
</s>
<s>
PDF	B-Application
files	I-Application
may	O
also	O
contain	O
embedded	O
DRM	O
restrictions	O
that	O
provide	O
further	O
controls	O
that	O
limit	O
copying	O
,	O
editing	O
,	O
or	O
printing	O
.	O
</s>
<s>
The	O
standard	O
security	O
provided	O
by	O
PDF	B-Application
consists	O
of	O
two	O
different	O
methods	O
and	O
two	O
different	O
passwords	O
:	O
a	O
user	O
password	O
,	O
which	O
encrypts	O
the	O
file	O
and	O
prevents	O
opening	O
,	O
and	O
an	O
owner	O
password	O
,	O
which	O
specifies	O
operations	O
that	O
should	O
be	O
restricted	O
even	O
when	O
the	O
document	O
is	O
decrypted	O
,	O
which	O
can	O
include	O
modifying	O
,	O
printing	O
,	O
or	O
copying	O
text	O
and	O
graphics	O
out	O
of	O
the	O
document	O
,	O
or	O
adding	O
or	O
modifying	O
text	O
notes	O
and	O
AcroForm	O
fields	O
.	O
</s>
<s>
Thus	O
,	O
the	O
use	O
restrictions	O
that	O
a	O
document	O
author	O
places	O
on	O
a	O
PDF	B-Application
document	O
are	O
not	O
secure	O
,	O
and	O
cannot	O
be	O
assured	O
once	O
the	O
file	O
is	O
distributed	O
;	O
this	O
warning	O
is	O
displayed	O
when	O
applying	O
such	O
restrictions	O
using	O
Adobe	B-Application
Acrobat	I-Application
software	O
to	O
create	O
or	O
edit	O
PDF	B-Application
files	I-Application
.	O
</s>
<s>
Even	O
without	O
removing	O
the	O
password	O
,	O
most	O
freeware	B-License
or	O
open	O
source	O
PDF	B-Language
readers	I-Language
ignore	O
the	O
permission	O
"	O
protections	O
"	O
and	O
allow	O
the	O
user	O
to	O
print	O
or	O
make	O
copy	O
of	O
excerpts	O
of	O
the	O
text	O
as	O
if	O
the	O
document	O
were	O
not	O
limited	O
by	O
password	O
protection	O
.	O
</s>
<s>
Beginning	O
with	O
PDF	B-Application
1.5	O
,	O
Usage	O
rights	O
(	O
UR	O
)	O
signatures	O
are	O
used	O
to	O
enable	O
additional	O
interactive	O
features	O
that	O
are	O
not	O
available	O
by	O
default	O
in	O
a	O
particular	O
PDF	B-Language
viewer	I-Language
application	O
.	O
</s>
<s>
For	O
example	O
,	O
Adobe	O
Systems	O
grants	O
permissions	O
to	O
enable	O
additional	O
features	O
in	O
Adobe	B-Application
Reader	I-Application
,	O
using	O
public-key	B-Application
cryptography	I-Application
.	O
</s>
<s>
Adobe	B-Application
Reader	I-Application
verifies	O
that	O
the	O
signature	O
uses	O
a	O
certificate	O
from	O
an	O
Adobe-authorized	O
certificate	O
authority	O
.	O
</s>
<s>
Any	O
PDF	B-Application
application	O
can	O
use	O
this	O
same	O
mechanism	O
for	O
its	O
own	O
purposes	O
.	O
</s>
<s>
PAdES	O
(	O
PDF	B-Application
Advanced	O
Electronic	O
Signatures	O
)	O
is	O
a	O
set	O
of	O
restrictions	O
and	O
extensions	O
to	O
PDF	B-Application
and	O
ISO	B-Application
32000-1	I-Application
making	O
it	O
suitable	O
for	O
advanced	O
electronic	O
signatures	O
.	O
</s>
<s>
PDF	B-Application
files	I-Application
can	O
have	O
file	O
attachments	O
which	O
processors	O
may	O
access	O
and	O
open	O
or	O
save	O
to	O
a	O
local	O
filesystem	O
.	O
</s>
<s>
PDF	B-Application
files	I-Application
can	O
contain	O
two	O
types	O
of	O
metadata	O
.	O
</s>
<s>
The	O
first	O
is	O
the	O
Document	O
Information	O
Dictionary	B-Application
,	O
a	O
set	O
of	O
key/value	O
fields	O
such	O
as	O
author	O
,	O
title	O
,	O
subject	O
,	O
creation	O
and	O
update	O
dates	O
.	O
</s>
<s>
This	O
method	O
is	O
deprecated	O
in	O
PDF	B-Application
2.0	O
.	O
</s>
<s>
In	O
PDF	B-Application
1.4	O
,	O
support	O
was	O
added	O
for	O
Metadata	O
Streams	B-Architecture
,	O
using	O
the	O
Extensible	O
Metadata	O
Platform	O
(	O
XMP	O
)	O
to	O
add	O
XML	O
standards-based	O
extensible	O
metadata	O
as	O
used	O
in	O
other	O
file	O
formats	O
.	O
</s>
<s>
PDF	B-Application
2.0	O
allows	O
metadata	O
to	O
be	O
attached	O
to	O
any	O
object	O
in	O
the	O
document	O
,	O
such	O
as	O
information	O
about	O
embedded	O
illustrations	O
,	O
fonts	O
,	O
and	O
images	O
,	O
as	O
well	O
as	O
the	O
whole	O
document	O
(	O
attaching	O
to	O
the	O
document	O
catalog	O
)	O
,	O
using	O
an	O
extensible	O
schema	O
.	O
</s>
<s>
PDF	B-Application
documents	I-Application
can	O
also	O
contain	O
display	O
settings	O
,	O
including	O
the	O
page	O
display	O
layout	O
and	O
zoom	O
level	O
in	O
a	O
Viewer	O
Preferences	O
object	O
.	O
</s>
<s>
Adobe	B-Application
Reader	I-Application
uses	O
these	O
settings	O
to	O
override	O
the	O
user	O
's	O
default	O
settings	O
when	O
opening	O
the	O
document	O
.	O
</s>
<s>
The	O
free	O
Adobe	B-Application
Reader	I-Application
cannot	O
remove	O
these	O
settings	O
.	O
</s>
<s>
PDF	B-Application
files	I-Application
can	O
be	O
created	O
specifically	O
to	O
be	O
accessible	O
for	O
people	O
with	O
disabilities	O
.	O
</s>
<s>
PDF	B-Application
file	I-Application
formats	O
in	O
use	O
can	O
include	O
tags	O
,	O
text	O
equivalents	O
,	O
captions	O
,	O
audio	O
descriptions	O
,	O
and	O
more	O
.	O
</s>
<s>
Some	O
software	O
can	O
automatically	O
produce	O
tagged	B-General_Concept
PDFs	I-General_Concept
,	O
but	O
this	O
feature	O
is	O
not	O
always	O
enabled	O
by	O
default	O
.	O
</s>
<s>
Leading	O
screen	O
readers	O
,	O
including	O
JAWS	B-Application
,	O
Window-Eyes	B-Device
,	O
Hal	O
,	O
and	O
Kurzweil	O
1000	O
and	O
3000	O
can	O
read	O
tagged	O
PDF	B-Application
.	O
</s>
<s>
Moreover	O
,	O
tagged	B-General_Concept
PDFs	I-General_Concept
can	O
be	O
re-flowed	O
and	O
magnified	O
for	O
readers	O
with	O
visual	O
impairments	O
.	O
</s>
<s>
Adding	O
tags	O
to	O
older	O
PDFs	B-Application
and	O
those	O
that	O
are	O
generated	O
from	O
scanned	O
documents	O
can	O
present	O
some	O
challenges	O
.	O
</s>
<s>
One	O
of	O
the	O
significant	O
challenges	O
with	O
PDF	B-Application
accessibility	O
is	O
that	O
PDF	B-Application
documents	I-Application
have	O
three	O
distinct	O
views	O
,	O
which	O
,	O
depending	O
on	O
the	O
document	O
's	O
creation	O
,	O
can	O
be	O
inconsistent	O
with	O
each	O
other	O
.	O
</s>
<s>
The	O
physical	O
view	O
is	O
displayed	O
and	O
printed	O
(	O
what	O
most	O
people	O
consider	O
a	O
PDF	B-Application
document	O
)	O
.	O
</s>
<s>
The	O
content	O
view	O
is	O
based	O
on	O
the	O
physical	O
order	O
of	O
objects	O
within	O
the	O
PDF	B-Application
's	O
content	O
stream	O
and	O
may	O
be	O
displayed	O
by	O
software	O
that	O
does	O
not	O
fully	O
support	O
the	O
tags	O
 '	O
view	O
,	O
such	O
as	O
the	O
Reflow	O
feature	O
in	O
Adobe	O
's	O
Reader	O
.	O
</s>
<s>
PDF/UA	B-Protocol
,	O
the	O
International	O
Standard	O
for	O
accessible	O
PDF	B-Application
based	O
on	O
ISO	B-Application
32000-1	I-Application
was	O
first	O
published	O
as	O
ISO	B-Protocol
14289	I-Protocol
–	O
1	O
in	O
2012	O
and	O
establishes	O
normative	O
language	O
for	O
accessible	O
PDF	B-Application
technology	O
.	O
</s>
<s>
Rich	O
Media	O
PDF	B-Application
is	O
a	O
PDF	B-Application
file	I-Application
including	O
interactive	O
content	O
that	O
can	O
be	O
embedded	O
or	O
linked	O
within	O
the	O
file	O
.	O
</s>
<s>
For	O
example	O
,	O
if	O
the	O
interactive	O
PDF	B-Application
is	O
a	O
digital	O
catalog	O
for	O
an	O
E-commerce	O
business	O
,	O
products	O
can	O
be	O
listed	O
on	O
the	O
PDF	B-Application
pages	O
and	O
can	O
be	O
added	O
with	O
images	O
and	O
links	O
to	O
the	O
website	O
and	O
buttons	O
to	O
order	O
directly	O
from	O
the	O
document	O
.	O
</s>
<s>
Interactive	O
Forms	O
is	O
a	O
mechanism	O
to	O
add	O
forms	O
to	O
the	O
PDF	B-Application
file	I-Application
format	O
.	O
</s>
<s>
PDF	B-Application
currently	O
supports	O
two	O
different	O
methods	O
for	O
integrating	O
data	O
and	O
PDF	B-Application
forms	O
.	O
</s>
<s>
Both	O
formats	O
today	O
coexist	O
in	O
the	O
PDF	B-Application
specification	O
:	O
</s>
<s>
AcroForms	O
(	O
also	O
known	O
as	O
Acrobat	B-Application
forms	I-Application
)	O
,	O
introduced	O
in	O
the	O
PDF	B-Application
1.2	O
format	O
specification	O
and	O
included	O
in	O
all	O
later	O
PDF	B-Application
specifications	O
.	O
</s>
<s>
XML	B-Language
Forms	I-Language
Architecture	I-Language
(	O
XFA	B-Language
)	O
forms	O
,	O
introduced	O
in	O
the	O
PDF	B-Application
1.5	O
format	O
specification	O
.	O
</s>
<s>
Adobe	O
XFA	B-Language
Forms	I-Language
are	O
not	O
compatible	O
with	O
AcroForms	O
.	O
</s>
<s>
XFA	B-Language
was	O
deprecated	O
from	O
PDF	B-Application
with	O
PDF	B-Application
2.0	O
.	O
</s>
<s>
AcroForms	O
were	O
introduced	O
in	O
the	O
PDF	B-Application
1.2	O
format	O
.	O
</s>
<s>
JavaScript	B-Language
)	O
.	O
</s>
<s>
Alongside	O
the	O
standard	O
PDF	B-Application
action	O
types	O
,	O
interactive	O
forms	O
(	O
AcroForms	O
)	O
support	O
submitting	O
,	O
resetting	O
,	O
and	O
importing	O
data	O
.	O
</s>
<s>
Forms	O
Data	O
Format	O
(	O
FDF	O
)	O
based	O
on	O
PDF	B-Application
,	O
uses	O
the	O
same	O
syntax	O
and	O
has	O
essentially	O
the	O
same	O
file	O
structure	O
,	O
but	O
is	O
much	O
simpler	O
than	O
PDF	B-Application
since	O
the	O
body	O
of	O
an	O
FDF	O
document	O
consists	O
of	O
only	O
one	O
required	O
object	O
.	O
</s>
<s>
Forms	O
Data	O
Format	O
is	O
defined	O
in	O
the	O
PDF	B-Application
specification	O
(	O
since	O
PDF	B-Application
1.2	O
)	O
.	O
</s>
<s>
It	O
can	O
also	O
be	O
used	O
to	O
export	O
form	O
data	O
to	O
stand-alone	O
files	O
that	O
can	O
be	O
imported	O
back	O
into	O
the	O
corresponding	O
PDF	B-Application
interactive	O
form	O
.	O
</s>
<s>
XML	O
Forms	O
Data	O
Format	O
(	O
XFDF	O
)	O
(	O
external	O
XML	O
Forms	O
Data	O
Format	O
Specification	O
,	O
Version	O
2.0	O
;	O
supported	O
since	O
PDF	B-Application
1.5	O
;	O
it	O
replaced	O
the	O
"	O
XML	O
"	O
form	O
submission	O
format	O
defined	O
in	O
PDF	B-Application
1.4	O
)	O
the	O
XML	O
version	O
of	O
Forms	O
Data	O
Format	O
,	O
but	O
the	O
XFDF	O
implements	O
only	O
a	O
subset	O
of	O
FDF	O
containing	O
forms	O
and	O
annotations	O
.	O
</s>
<s>
Some	O
entries	O
in	O
the	O
FDF	O
dictionary	B-Application
do	O
not	O
have	O
XFDF	O
equivalents	O
–	O
such	O
as	O
the	O
Status	O
,	O
Encoding	O
,	O
JavaScript	B-Language
,	O
Page	O
's	O
keys	O
,	O
EmbeddedFDFs	O
,	O
Differences	O
,	O
and	O
Target	O
.	O
</s>
<s>
The	O
XFDF	O
specification	O
is	O
referenced	O
(	O
but	O
not	O
included	O
)	O
in	O
PDF	B-Application
1.5	O
specification	O
(	O
and	O
in	O
later	O
versions	O
)	O
.	O
</s>
<s>
The	O
PDF	B-Application
1.4	O
specification	O
allowed	O
form	O
submissions	O
in	O
XML	O
format	O
,	O
but	O
this	O
was	O
replaced	O
by	O
submissions	O
in	O
XFDF	O
format	O
in	O
the	O
PDF	B-Application
1.5	O
specification	O
.	O
</s>
<s>
It	O
can	O
also	O
be	O
used	O
to	O
export	O
form	O
data	O
to	O
stand-alone	O
files	O
that	O
can	O
be	O
imported	O
back	O
into	O
the	O
corresponding	O
PDF	B-Application
interactive	O
form	O
.	O
</s>
<s>
As	O
of	O
August	O
2019	O
,	O
XFDF	O
3.0	O
is	O
an	O
ISO/IEC	O
standard	O
under	O
the	O
formal	O
name	O
ISO	B-General_Concept
19444-1:2019	O
-	O
Document	O
management	O
—	O
XML	O
Forms	O
Data	O
Format	O
—	O
Part	O
1	O
:	O
Use	O
of	O
ISO	B-General_Concept
32000-2	O
(	O
XFDF	O
3.0	O
)	O
.	O
</s>
<s>
The	O
entire	O
document	O
can	O
be	O
submitted	O
rather	O
than	O
individual	O
fields	O
and	O
values	O
,	O
as	O
was	O
defined	O
in	O
PDF	B-Application
1.4	O
.	O
</s>
<s>
The	O
usage	O
rights	O
(	O
UR	O
)	O
signatures	O
define	O
rights	O
for	O
import	O
form	O
data	O
files	O
in	O
FDF	O
,	O
XFDF	O
,	O
and	O
text	O
(	O
CSV/TSV	O
)	O
formats	O
,	O
and	O
export	O
form	O
data	O
files	O
in	O
FDF	O
and	O
XFDF	O
formats	O
.	O
</s>
<s>
In	O
PDF	B-Application
1.5	O
,	O
Adobe	O
Systems	O
introduced	O
a	O
proprietary	O
format	O
for	O
forms	O
;	O
Adobe	B-Language
XML	I-Language
Forms	I-Language
Architecture	I-Language
(	O
XFA	B-Language
)	O
.	O
</s>
<s>
Adobe	O
XFA	B-Language
Forms	I-Language
are	O
not	O
compatible	O
with	O
ISO	B-Application
32000	I-Application
's	O
AcroForms	O
feature	O
,	O
and	O
most	O
PDF	B-Application
processors	O
do	O
not	O
handle	O
XFA	B-Language
content	O
.	O
</s>
<s>
The	O
XFA	B-Language
specification	O
is	O
referenced	O
from	O
ISO	O
32000-1/PDF	O
1.7	O
as	O
an	O
external	O
proprietary	O
specification	O
and	O
was	O
entirely	O
deprecated	O
from	O
PDF	B-Application
with	O
ISO	O
32000-2	O
(	O
PDF	B-Application
2.0	O
)	O
.	O
</s>
<s>
Anyone	O
may	O
create	O
applications	O
that	O
can	O
read	O
and	O
write	O
PDF	B-Application
files	I-Application
without	O
having	O
to	O
pay	O
royalties	O
to	O
Adobe	O
Systems	O
;	O
Adobe	O
holds	O
patents	O
to	O
PDF	B-Application
,	O
but	O
licenses	O
them	O
for	O
royalty-free	O
use	O
in	O
developing	O
software	O
complying	O
with	O
its	O
PDF	B-Application
specification	O
.	O
</s>
<s>
In	O
November	O
2019	O
,	O
researchers	O
from	O
Ruhr	O
University	O
Bochum	O
and	O
Hackmanit	O
GmbH	O
published	O
attacks	O
on	O
digitally	O
signed	O
PDFs	B-Application
.	O
</s>
<s>
They	O
showed	O
how	O
to	O
change	O
the	O
visible	O
content	O
in	O
a	O
signed	O
PDF	B-Application
without	O
invalidating	O
the	O
signature	O
in	O
21	O
of	O
22	O
desktop	O
PDF	B-Language
viewers	I-Language
and	O
6	O
of	O
8	O
online	O
validation	O
services	O
by	O
abusing	O
implementation	O
flaws	O
.	O
</s>
<s>
At	O
the	O
same	O
conference	O
,	O
they	O
additionally	O
showed	O
how	O
to	O
exfiltrate	O
the	O
plaintext	O
of	O
encrypted	O
content	O
in	O
PDFs	B-Application
.	O
</s>
<s>
In	O
2021	O
,	O
they	O
showed	O
new	O
so-called	O
shadow	O
attacks	O
on	O
PDFs	B-Application
that	O
abuse	O
the	O
flexibility	O
of	O
features	O
provided	O
in	O
the	O
specification	O
.	O
</s>
<s>
An	O
overview	O
of	O
security	O
issues	O
in	O
PDFs	B-Application
regarding	O
denial	O
of	O
service	O
,	O
information	O
disclosure	O
,	O
data	O
manipulation	O
,	O
and	O
Arbitrary	O
code	O
execution	O
attacks	O
was	O
presented	O
by	O
Jens	O
Müller	O
.	O
</s>
<s>
PDF	B-Application
attachments	O
carrying	O
viruses	O
were	O
first	O
discovered	O
in	O
2001	O
.	O
</s>
<s>
The	O
virus	O
,	O
named	O
OUTLOOK.PDFWorm	O
or	O
Peachy	O
,	O
uses	O
Microsoft	B-Application
Outlook	I-Application
to	O
send	O
itself	O
as	O
an	O
attached	O
Adobe	B-Application
PDF	I-Application
file	O
.	O
</s>
<s>
It	O
was	O
activated	O
with	O
Adobe	B-Application
Acrobat	I-Application
,	O
but	O
not	O
with	O
Acrobat	B-Application
Reader	I-Application
.	O
</s>
<s>
From	O
time	O
to	O
time	O
,	O
new	O
vulnerabilities	O
are	O
discovered	O
in	O
various	O
versions	O
of	O
Adobe	B-Application
Reader	I-Application
,	O
prompting	O
the	O
company	O
to	O
issue	O
security	O
fixes	O
.	O
</s>
<s>
Other	O
PDF	B-Language
readers	I-Language
are	O
also	O
susceptible	O
.	O
</s>
<s>
One	O
aggravating	O
factor	O
is	O
that	O
a	O
PDF	B-Language
reader	I-Language
can	O
be	O
configured	O
to	O
start	O
automatically	O
if	O
a	O
web	O
page	O
has	O
an	O
embedded	O
PDF	B-Application
file	I-Application
,	O
providing	O
a	O
vector	O
for	O
attack	O
.	O
</s>
<s>
If	O
a	O
malicious	O
web	O
page	O
contains	O
an	O
infected	O
PDF	B-Application
file	I-Application
that	O
takes	O
advantage	O
of	O
a	O
vulnerability	O
in	O
the	O
PDF	B-Language
reader	I-Language
,	O
the	O
system	O
may	O
be	O
compromised	O
even	O
if	O
the	O
browser	O
is	O
secure	O
.	O
</s>
<s>
Some	O
of	O
these	O
vulnerabilities	O
are	O
a	O
result	O
of	O
the	O
PDF	B-Application
standard	O
allowing	O
PDF	B-Application
documents	I-Application
to	O
be	O
scripted	O
with	O
JavaScript	B-Language
.	O
</s>
<s>
Disabling	O
JavaScript	B-Language
execution	O
in	O
the	O
PDF	B-Language
reader	I-Language
can	O
help	O
mitigate	O
such	O
future	O
exploits	O
,	O
although	O
it	O
does	O
not	O
protect	O
against	O
exploits	O
in	O
other	O
parts	O
of	O
the	O
PDF	B-Application
viewing	O
software	O
.	O
</s>
<s>
Security	O
experts	O
say	O
that	O
JavaScript	B-Language
is	O
not	O
essential	O
for	O
a	O
PDF	B-Language
reader	I-Language
and	O
that	O
the	O
security	O
benefit	O
that	O
comes	O
from	O
disabling	O
JavaScript	B-Language
outweighs	O
any	O
compatibility	O
issues	O
caused	O
.	O
</s>
<s>
One	O
way	O
of	O
avoiding	O
PDF	B-Application
file	I-Application
exploits	O
is	O
to	O
have	O
a	O
local	O
or	O
web	O
service	O
convert	O
files	O
to	O
another	O
format	O
before	O
viewing	O
.	O
</s>
<s>
On	O
March	O
30	O
,	O
2010	O
,	O
security	O
researcher	O
Didier	O
Stevens	O
reported	O
an	O
Adobe	B-Application
Reader	I-Application
and	O
Foxit	B-Language
Reader	I-Language
exploit	O
that	O
runs	O
a	O
malicious	O
executable	O
if	O
the	O
user	O
allows	O
it	O
to	O
launch	O
when	O
asked	O
.	O
</s>
<s>
PDF	B-Language
viewers	I-Language
are	O
generally	O
provided	O
free	O
of	O
charge	O
,	O
and	O
many	O
versions	O
are	O
available	O
from	O
a	O
variety	O
of	O
sources	O
.	O
</s>
<s>
There	O
are	O
many	O
software	O
options	O
for	O
creating	O
PDFs	B-Application
,	O
including	O
the	O
PDF	B-Application
printing	O
capabilities	O
built	O
into	O
macOS	B-Application
,	O
iOS	B-Application
,	O
and	O
most	O
Linux	B-Application
distributions	O
,	O
LibreOffice	B-Application
,	O
Microsoft	B-Application
Office	I-Application
2007	I-Application
(	O
if	O
updated	O
to	O
SP2	O
)	O
and	O
later	O
,	O
WordPerfect	B-Application
9	O
,	O
Scribus	B-Application
,	O
numerous	O
PDF	B-Application
print	O
drivers	O
for	O
Microsoft	B-Application
Windows	I-Application
,	O
the	O
pdfTeX	B-Language
typesetting	O
system	O
,	O
the	O
DocBook	B-Protocol
PDF	B-Application
tools	O
,	O
applications	O
developed	O
around	O
Ghostscript	B-Language
and	O
Adobe	B-Application
Acrobat	I-Application
itself	O
as	O
well	O
as	O
Adobe	B-Operating_System
InDesign	I-Operating_System
,	O
Adobe	B-Device
FrameMaker	I-Device
,	O
Adobe	B-Language
Illustrator	I-Language
,	O
Adobe	B-Operating_System
Photoshop	I-Operating_System
.	O
</s>
<s>
Google	B-Application
's	I-Application
online	O
office	O
suite	O
Google	B-Application
Docs	I-Application
allows	O
for	O
uploading	O
and	O
saving	O
to	O
PDF	B-Application
.	O
</s>
<s>
Some	O
web	O
apps	O
offer	O
free	O
PDF	B-Application
editing	O
and	O
annotation	O
tools	O
.	O
</s>
<s>
The	B-Operating_System
Free	I-Operating_System
Software	I-Operating_System
Foundation	I-Operating_System
once	O
thought	O
of	O
as	O
one	O
of	O
their	O
high	O
priority	O
projects	O
to	O
be	O
"	O
developing	O
a	O
free	O
,	O
high-quality	O
and	O
fully	O
functional	O
set	O
of	O
libraries	O
and	O
programs	O
that	O
implement	O
the	O
PDF	B-Application
file	I-Application
format	O
and	O
associated	O
technologies	O
to	O
the	O
ISO	B-Application
32000	I-Application
standard.	O
"	O
</s>
<s>
In	O
2011	O
,	O
however	O
,	O
the	O
GNU	O
PDF	B-Application
project	O
was	O
removed	O
from	O
the	O
list	O
of	O
"	O
high	O
priority	O
projects	O
"	O
due	O
to	O
the	O
maturation	O
of	O
the	O
Poppler	B-Language
library	I-Language
,	O
which	O
has	O
enjoyed	O
wider	O
use	O
in	O
applications	O
such	O
as	O
Evince	B-Language
with	O
the	O
GNOME	B-Application
desktop	I-Application
environment	I-Application
.	O
</s>
<s>
Poppler	B-Language
is	O
based	O
on	O
Xpdf	B-Protocol
code	O
base	O
.	O
</s>
<s>
There	O
are	O
also	O
commercial	O
development	O
libraries	O
available	O
as	O
listed	O
in	O
List	B-Language
of	I-Language
PDF	I-Language
software	I-Language
.	O
</s>
<s>
The	O
Apache	B-Language
PDFBox	I-Language
project	O
of	O
the	O
Apache	O
Software	O
Foundation	O
is	O
an	O
open	O
source	O
Java	O
library	O
for	O
working	O
with	O
PDF	B-Application
documents	I-Application
.	O
</s>
<s>
PDFBox	B-Language
is	O
licensed	O
under	O
the	O
Apache	B-Application
License	I-Application
.	O
</s>
<s>
Raster	B-Algorithm
image	I-Algorithm
processors	O
(	O
RIPs	O
)	O
are	O
used	O
to	O
convert	O
PDF	B-Application
files	I-Application
into	O
a	O
raster	B-Algorithm
format	I-Algorithm
suitable	O
for	O
imaging	O
onto	O
paper	O
and	O
other	O
media	O
in	O
printers	O
,	O
digital	O
production	O
presses	O
and	O
prepress	O
in	O
a	O
process	O
known	O
as	O
rasterization	O
.	O
</s>
<s>
RIPs	O
capable	O
of	O
processing	O
PDF	B-Application
directly	O
include	O
the	O
Adobe	B-Application
PDF	I-Application
Print	O
Engine	O
from	O
Adobe	O
Systems	O
and	O
Jaws	B-Application
and	O
the	O
Harlequin	B-Language
RIP	I-Language
from	O
Global	O
Graphics	O
.	O
</s>
<s>
In	O
1993	O
,	O
the	O
Jaws	B-Application
raster	B-Algorithm
image	I-Algorithm
processor	O
from	O
Global	O
Graphics	O
became	O
the	O
first	O
shipping	O
prepress	O
RIP	O
that	O
interpreted	O
PDF	B-Application
natively	O
without	O
conversion	O
to	O
another	O
format	O
.	O
</s>
<s>
The	O
company	O
released	O
an	O
upgrade	O
to	O
their	O
Harlequin	B-Language
RIP	I-Language
with	O
the	O
same	O
capability	O
in	O
1997	O
.	O
</s>
<s>
Agfa-Gevaert	O
introduced	O
and	O
shipped	O
Apogee	O
,	O
the	O
first	O
prepress	O
workflow	B-Operating_System
system	O
based	O
on	O
PDF	B-Application
,	O
in	O
1997	O
.	O
</s>
<s>
Many	O
commercial	O
offset	O
printers	O
have	O
accepted	O
the	O
submission	O
of	O
press-ready	O
PDF	B-Application
files	I-Application
as	O
a	O
print	O
source	O
,	O
specifically	O
the	O
PDF/X	O
-1a	O
subset	O
and	O
variations	O
of	O
the	O
same	O
.	O
</s>
<s>
The	O
submission	O
of	O
press-ready	O
PDF	B-Application
files	I-Application
is	O
a	O
replacement	O
for	O
the	O
problematic	O
need	O
for	O
receiving	O
collected	O
native	O
working	O
files	O
.	O
</s>
<s>
In	O
2006	O
,	O
PDF	B-Application
was	O
widely	O
accepted	O
as	O
the	O
standard	O
print	O
job	O
format	O
at	O
the	O
Open	O
Source	O
Development	O
Labs	O
Printing	O
Summit	O
.	O
</s>
<s>
It	O
is	O
supported	O
as	O
a	O
print	O
job	O
format	O
by	O
the	O
Common	O
Unix	O
Printing	O
System	O
and	O
desktop	B-Application
application	I-Application
projects	O
such	O
as	O
GNOME	B-Application
,	O
KDE	B-Application
,	O
Firefox	B-Application
,	O
Thunderbird	B-Application
,	O
LibreOffice	B-Application
and	O
OpenOffice	B-Application
have	O
switched	O
to	O
emit	O
print	O
jobs	O
in	O
PDF	B-Application
.	O
</s>
<s>
Some	O
desktop	O
printers	O
also	O
support	O
direct	O
PDF	B-Application
printing	O
,	O
which	O
can	O
interpret	O
PDF	B-Application
data	O
without	O
external	O
help	O
.	O
</s>
<s>
PDF	B-Application
was	O
selected	O
as	O
the	O
"	O
native	O
"	O
metafile	O
format	O
for	O
Mac	B-Application
OS	I-Application
X	I-Application
,	O
replacing	O
the	O
PICT	B-Language
format	O
of	O
the	O
earlier	O
classic	B-Application
Mac	I-Application
OS	I-Application
.	O
</s>
<s>
The	O
imaging	O
model	O
of	O
the	O
Quartz	B-Operating_System
graphics	O
layer	O
is	O
based	O
on	O
the	O
model	O
common	O
to	O
Display	O
PostScript	B-Language
and	O
PDF	B-Application
,	O
leading	O
to	O
the	O
nickname	O
Display	B-Application
PDF	I-Application
.	O
</s>
<s>
The	O
Preview	O
application	O
can	O
display	B-Application
PDF	I-Application
files	O
,	O
as	O
can	O
version	O
2.0	O
and	O
later	O
of	O
the	O
Safari	B-Application
web	I-Application
browser	I-Application
.	O
</s>
<s>
System-level	O
support	O
for	O
PDF	B-Application
allows	O
Mac	B-Application
OS	I-Application
X	I-Application
applications	O
to	O
create	O
PDF	B-Application
documents	I-Application
automatically	O
,	O
provided	O
they	O
support	O
the	O
OS-standard	O
printing	O
architecture	O
.	O
</s>
<s>
The	O
files	O
are	O
then	O
exported	O
in	O
PDF	B-Application
1.3	O
format	O
according	O
to	O
the	O
file	O
header	O
.	O
</s>
<s>
When	O
taking	O
a	O
screenshot	O
under	O
Mac	B-Application
OS	I-Application
X	I-Application
versions	O
10.0	O
through	O
10.3	O
,	O
the	O
image	O
was	O
also	O
captured	O
as	O
a	O
PDF	B-Application
;	O
later	O
versions	O
save	O
screen	O
captures	O
as	O
a	O
PNG	O
file	O
,	O
though	O
this	O
behavior	O
can	O
be	O
set	O
back	O
to	O
PDF	B-Application
if	O
desired	O
.	O
</s>
<s>
Adobe	B-Application
Acrobat	I-Application
is	O
one	O
example	O
of	O
proprietary	O
software	O
that	O
allows	O
the	O
user	O
to	O
annotate	O
,	O
highlight	O
,	O
and	O
add	O
notes	O
to	O
already	O
created	O
PDF	B-Application
files	I-Application
.	O
</s>
<s>
One	O
UNIX	O
application	O
available	O
as	O
free	B-Application
software	I-Application
(	O
under	O
the	O
GNU	B-License
General	I-License
Public	I-License
License	I-License
)	O
is	O
PDFedit	B-Language
.	O
</s>
<s>
The	O
freeware	B-License
Foxit	B-Language
Reader	I-Language
,	O
available	O
for	O
Microsoft	B-Application
Windows	I-Application
,	O
macOS	B-Application
and	O
Linux	B-Application
,	O
allows	O
annotating	O
documents	O
.	O
</s>
<s>
Tracker	O
Software	O
's	O
PDF-XChange	B-Application
Viewer	I-Application
allows	O
annotations	O
and	O
markups	O
without	O
restrictions	O
in	O
its	O
freeware	B-License
alternative	O
.	O
</s>
<s>
Apple	O
's	O
macOS	B-Application
's	O
integrated	O
PDF	B-Language
viewer	I-Language
,	O
Preview	O
,	O
does	O
also	O
enable	O
annotations	O
as	O
does	O
the	O
open-source	O
software	O
Skim	B-Language
,	O
with	O
the	O
latter	O
supporting	O
interaction	O
with	O
LaTeX	B-Application
,	O
SyncTeX	O
,	O
and	O
PDFSync	O
and	O
integration	O
with	O
BibDesk	B-Language
reference	O
management	O
software	O
.	O
</s>
<s>
Freeware	B-License
Qiqqa	B-Application
can	O
create	O
an	O
annotation	O
report	O
that	O
summarizes	O
all	O
the	O
annotations	O
and	O
notes	O
one	O
has	O
made	O
across	O
their	O
library	O
of	O
PDFs	B-Application
.	O
</s>
<s>
There	O
are	O
also	O
web	B-Protocol
annotation	I-Protocol
systems	O
that	O
support	O
annotation	O
in	O
pdf	B-Application
and	O
other	O
documents	O
formats	O
.	O
</s>
<s>
In	O
cases	O
where	O
PDFs	B-Application
are	O
expected	O
to	O
have	O
all	O
of	O
the	O
functionality	O
of	O
paper	O
documents	O
,	O
ink	O
annotation	O
is	O
required	O
.	O
</s>
<s>
The	O
Open	B-Device
XML	I-Device
Paper	I-Device
Specification	I-Device
is	O
a	O
competing	O
format	O
used	O
both	O
as	O
a	O
page	O
description	O
language	O
and	O
as	O
the	O
native	O
print	O
spooler	O
format	O
for	O
Microsoft	B-Application
Windows	I-Application
since	O
Windows	B-Application
Vista	I-Application
.	O
</s>
<s>
MO:DCA-P	O
is	O
a	O
part	O
of	O
Advanced	B-Application
Function	I-Application
Presentation	I-Application
.	O
</s>
